Alpha-Bungarotoxin (alpha-Bgt) has been one of the most frequently used alpha-toxin probes for studies of nicotinic acetylcholine receptors (NaChR). Alpha-Bgt exhibits high affinity binding to the putative AChR of the mammalian CNS as well as to peripheral nAChR. The binding components have many characteristics in common. However, the identity of the alpha-Bgt binding sites in mammalian CNS has been questioned. We propose to isolate, characterize, and label with 125I and 3H, alpha-toxins which are as yet little studied. The sources include the crude venoms from Bungarus multicinctus and Dendroaspis viridis. We believe alpha-toxins from these sources may be uniquely useful for studies of the mammalian CNS AChR. The binding of these alpha-toxins will be studied with receptors from a variety of sources including mammalian and chicken brain, rodent and calf retina, and electroplax. The ultimate aim is to provide fundamental information concerning structure and properties of AChR, and to provide further data comparing the peripheral nAChR with the putative nAChR of the mammalian CNS.